Can MySQL Join Tables Across Different Databases?

Performing Inter-Database Joins in MySQL

In MySQL, you may encounter scenarios where you need to join tables from different databases. This article will delve into the possibility of performing such joins, providing the necessary syntax and guidelines.

Question: Is it possible to join tables from two different databases in MySQL?

Answer: Yes, it is possible to perform inter-database joins in MySQL.

Syntax:

SELECT <column_list>
FROM <db_name1>.<table_name1> <alias1>
JOIN <db_name2>.<table_name2> <alias2>
ON <alias1>.<column_name> = <alias2>.<column_name>

Explanation:

• Prefix each table reference with its corresponding database name.
• Use table aliases to distinguish between tables from different databases.
• Specify the join condition using the ON clause.

Example:

Consider two databases, A and B, with tables table1 and table2, respectively. To join these tables, you can use the following query:

SELECT *
FROM A.table1 t1 JOIN B.table2 t2 ON t2.column2 = t1.column1;

Note:

• Ensure that the user account has the necessary permissions to access both databases and tables.
• The joined columns must have compatible data types and sizes.
• Inter-database joins can affect performance and resource usage, so optimize the query accordingly.

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